In the field of magnetic resonance imaging (“MRI”) it can be desirable to achieve a high signal-to-noise ratio (“SNR”). One technique for obtaining a higher SNR is to increase the magnetic field strength. As magnetic fields increase in strength, various problems may arise, some of which can compromise the advantages of higher-field MRI. One of these problems is dielectric resonance, which can occur when a resonance wavelength is comparable to a dimension of the human body.
Wave effects of electromagnetic fields (“EMF”) can make it difficult to achieve global homogeneous excitation. This may cause images of some areas of the body to appear overly darkened and other areas to appear overly brightened. Presently, 3 T scanners are widely available in clinical settings around the world, but their coils are often affected by this problem, which can limit their use in various MRI applications. The dielectric resonance problem can be even more pronounced at higher magnetic fields (e.g., fields greater than 7.0 T). This problem is described, e.g., in Vaughn, J T, et al., Magnetic Resonance Med., 2001, 46:24.
Existing MRI methods may not adequately overcome the dielectric resonance problems. One conventional method of addressing dielectric resonance is to add an extra dielectric band around the body of a patient. However, this approach generally may not be well-controlled and must be applied on a case-by-case basis.
Thus there exists a need to provide an improved magnetic resonance imaging method and system which overcomes at least some of the above-referenced deficiencies.